Raman spectroscopy for quantifying cholesterol in intact coronary artery wall

The chemical composition of vascular lesions, an important determinant of p laque progression and rupture, can not presently be determined in vivo. Pri or studies have shown that Raman spectroscopy can accurately quantify the a mounts of major lipid classes and calcium salts in homogenized coronary art ery tissue. This study determines how the relative cholesterol content, whi ch is calculated from Raman spectra collected at the luminal surface of an artery, is related to its depth in an intact arterial wall. Raman spectra o f human atherosclerotic plaques were measured after thin tissue layers were successively placed on them. From these spectra, relative cholesterol cont ents were calculated and used to determine how cholesterol signal strength is attenuated by overlaying tissue. Then, intact artery samples (n = 13) we re examined spectroscopically, sectioned and stained specifically for chole sterol. Images of these sections were digitized, and image intensities were related to cholesterol content. These cholesterol amounts were weighed app ropriately for depth into the tissue and area-integrated for comparison wit h spectroscopy results. A decaying exponential curve was fit to the layer s tudy data (r(2) = 0.97) and showed that similar to 300 mu m of tissue atten uates cholesterol signals by 50%. In intact plaques, the spectroscopically- determined cholesterol amounts correlated strongly and linearly with those determined by digital microscopy (r(2) = 0.94). With Raman spectroscopy tec hniques, the cholesterol content of a lesion can be determined by properly accounting for its depth into an arterial wall. Our results suggest that ch emical concentrations in an artery wall could be mapped throughout its thic kness, possibly by combining Raman spectroscopy methods with other techniqu es. (C) 1998 Published by Elsevier Science Ireland Ltd. All rights reserved .